Cisco fixes critical authentication bypass bug with public exploit

Cisco has addressed an almost maximum severity authentication bypass Enterprise NFV Infrastructure Software (NFVIS) vulnerability with public proof-of-concept (PoC) exploit code.

The security flaw (tracked as CVE-2021-34746) was found in the TACACS+ authentication, authorization, and accounting (AAA) of Cisco's Enterprise NFV Infrastructure Software, a solution designed to help virtualize network services for easier management of virtual network functions (VNFs).

CVE-2021-34746 is caused by incomplete validation of user-supplied input passed to an authentication script during the sign-in process which allows unauthenticated, remote attackers to log into unpatched device as an administrator.

"An attacker could exploit this vulnerability by injecting parameters into an authentication request," Cisco explained in a security advisory published on Wednesday.

"A successful exploit could allow the attacker to bypass authentication and log in as an administrator to the affected device."

Not all Enterprise NFVIS devices are vulnerable

Enterprise NFVIS deployments are impacted by this vulnerability only if the TACACS external authentication method is enabled on a targeted device.

To check if a device is vulnerable to CVE-2021-34746 exploits, you must check if the TACACS external authentication feature is toggled on.

This can be done via the command line using the show running-config tacacs-server command (which should display "no entries found" when TACACS is disabled).

You can also use the GUI by going to Configuration > Host > Security > User and Roles and checking if the feature shows up under External Authentication.

Cisco said no workarounds are available to remove the attack vector exposed by this security flaw, but fixed the issue in Cisco Enterprise NFVIS releases 4.6.1 and later.

While the company's Product Security Incident Response Team (PSIRT) stated that proof-of-concept exploit code is available, it also added that it's not aware of any ongoing exploitation in the wild.

One month ago, Cisco revealed that it is still working on a patch for a remote code execution (RCE) zero-day vulnerability in the Adaptive Security Device Manager (ADSM) Launcher disclosed in July.